It is known to load mail pieces into clamps and then sort the mail pieces by interacting only with the clamps. A major benefit of such a sorter is to enable sorting a much wider latitude of mail piece types than can be sorted using current technology. The following related patent applications are incorporated herein by reference, in their entirety: U.S. Provisional Application No. 60/669,340 (filed 7 Apr. 2005), and also International Application US06/12861 (filed 7 Apr. 2006) which claims priority to the U.S. provisional application.
There are many ways that this sorting concept could be applied to mail processing applications. Those applications include using inward or outward sort algorithms to sort single types of mail (e.g. letters, flats, newspapers, or non-machineable mail), or merging these mail streams together and sorting. Many posts around the world continue to seek a more effective mail merging system that automatically merges all mail streams and sorts them to delivery sequence. The system should accomplish this merging at the step of carrier sequence sorting by merging all elements of the mail stream (letters, flats, periodicals, post cards etc) at the final sorting process. There continues to be a need to refine and optimize sorting configurations and algorithms to complete the task of sorting multiple routes of mail within finite time windows available at the posts. Typically, the posts would like to sort 20 to 30 routes of mail within a two-hour time frame.
At present, some of the mail streams arrive at the postal branch offices pre-sorted, and some do not. Generally, even when the mail arrives at the branch already sorted by delivery sequence, postal carriers need to merge multiple streams of mail (often as many as ten streams) from different mail trays—and for this the postal carriers generally use a manual sorting process. When mail does not arrive at the branch pre-sorted, the carriers spend even more time—several hours—sorting the mail into carrier delivery sequence manually. Often, the carrier on mechanized routes will complete the mail merging while sitting at each post box—merging mail from multiple mail trays on the spot before placing it in the mailbox. This requires carriers to spend substantial time merging and sorting the mail before they can start to deliver it, or else they must complete the merging while they are delivering the mail, thus making the mail delivery process (the last mile) quite inefficient.
The 2003 Presidential Commission Report on the Future of the United States Postal Service (USPS) concluded that the Postal Service should continue to develop an effective merging system that is responsive to customer needs and culminates in one bundle of mixed letters and flats for each delivery point. The system should accomplish this merging at the step of carrier sequence sorting by merging all elements of the mail stream (letters, flats, periodicals, post cards etc) at the final sorting process.
The sorters available on the market today have significant limitations: they are either huge, expensive pieces of equipment with a very large number of bins, and require significant space to operate; or they have a smaller number of bins, but require multiple passes to operate. This multi-pass operation is a very labor-intensive process. So, for example, a sorter with 16 bins, sorting a job to 2000 addresses, will require three passes. That means the operator must load the mail, operate the sorter, then unload the mail from each bin and re-load it into the feeder three times. While this results in some time savings compared to manual sorting, the value proposition is limited because of the high labor content. See, for example, U.S. Pat. No. 6,555,776 entitled “Single Feed One Pass Mixed Mail Sequencer,” filed 2 Apr. 2001 and issued 29 Apr. 2003.
International Application US06/12861 involves a clamp-based sorting system having a sort-to-route module as well as a sort-to-delivery-sequence module, in order to simultaneously sort inbound and outbound mail. However, International Application US06/12861 does not disclose any way to efficiently sort inbound mail that has already been sorted to route, and does not disclose a way to efficiently sort to any other degree of fineness. For example, in order to sort mail for one route to delivery sequence using the sort-to-delivery sequence modules, the equivalent of 800 address stations was assumed. That configuration has high productivity, but also high cost. Moreover, International Application US06/12861 requires that all the mail for the entire route must be read before starting the sorting step, which means that all this mail needs to be stored somewhere for a period of time prior to sorting. Thus, according to International Application US06/12861, the inbound mail is sorted to route and stored for a long time (up to a whole shift of 8 hours) before being re-cycled for a second pass through the sorter in the sort-to-delivery-sequence step. All the mail from each route must be read before the final sorting step (sort to delivery sequence) is started. Inherent in that related art approach is the same limitation: all the mail pieces for a route must be read before the sorting step can be started.
Each morning before delivering the mail, a postman normally will manually merge all the separate mail streams together, and sort them to delivery sequence. Typically, this task takes 2.5 to 3 hours to complete. It is also possible to do this job using two types of automated sorter configurations, such as the clamp-based systems mentioned above. One configuration has, for example, 80 address stations, while the second configuration has 800 address stations. For both of these configurations, all the mail for a specific route must be fed, read, and clamped before sorting begins. This is because the sorter controller needs to know the number of pieces destined for each address before assigning the temporary addresses to the individual sorting stations. Typically, the sort station would have a limited capacity for storing mail pieces. For example, in European routes, each address receives an average of 2.5 mail pieces per day. So, the sorter might be designed in such a way that each sorting station has the capacity to store 5 mail pieces. If any address is to receive more than 5 pieces on a particular day, the controller knows this before the sorting step begins, and simply assigns two or more adjacent sorting stations to that address. In this way, all of the mail can be sorted to delivery sequence without special handling for exceptions. If an address receives no mail pieces, the controller does not assign a sort station for that address. In this way, the total sorting path can be kept relatively short. An alternative would be to increase the storage capacity of each sort station to minimize the chances that on any day the capacity will be exceeded—but there will always be exceptions. And this approach makes the sorting path longer, and lengthens total job time for sorting.
In the first of the two types of automated sorter configurations, the unsorted mail makes multiple passes around a race track path. During each pass around the race track, the system controller assigns temporary address identifications to each sort station. As the unsorted mail is transported around the race track, all the mail pieces destined for the temporarily assigned addresses are diverted to the sort stations. The race track shaped path for unsorted mail in the 80 address station configuration has the capacity to transport 1500 mail pieces (for 600 addresses at 2.5 pieces per address) around a race track path for unsorted mail. During the first pass around the race track path, the mail for only the first 80 addresses would be diverted to the address stations. When the last of the unsorted mail passes the divert stations, the sorted mail is moved on a second path toward an unloading station. These emptied address stations are then assigned the next 80 addresses on the route. When the unsorted mail makes a second pass, the mail for the second 80 addresses is diverted to the address stations. This sorted mail is then cleared out of the second path and moved toward the unloading station, and the unsorted mail is transported past the 80 stations a third time, fourth time, et cetera—each time with the 80 sorting stations assigned a new batch of 80 addresses, until mail to all 600 addresses has been sorted. In this example, the unsorted mail will make 7.5 cycles around the inner path.
This first configuration is one of the lowest cost sorting options, but not a good option if fast job time is required. It takes about 30 minutes to sort one route's worth of mail. This is 5 to 6 times faster than the postman can sort the equivalent volume. But, it will take this sorter ten hours to sort 20 routes of mail—a typical application. Generally, posts only allow 2 to 3 hours to complete this job, and therefore 4 or more sorters would be required to sort every 20 routes total job within the time available.
The second alternative configuration completes sorting 20 routes' worth of mail in about 2 hours. This configuration has 800 diverters and temporarily assignable address stations, and multiple feed/read/clamp systems to input the mail into the sorter. With 800 diverters in the sorting path, each batch of unsorted mail (1500 pieces per route) will make only one pass through the sorter. The temporarily assignable address stations will need to be assigned addresses only once per route. And as soon as the last of the unsorted mail for any route's worth of mail passes by a diverter to an address station, that (sorted) mail can be moved by the second path toward an unload station—thereby making the addressing stations sequentially available for reassignment of new address destinations for the next route. In this situation, the mail for a second route can be fed in shortly after the last piece of the first route's mail has entered the sorter. And a third route's worth of mail can enter right behind the second, and so forth. Each batch of mail makes only a single pass through the sorter, and all the mail is sorted to 600 to 800 addresses on a single pass.
According to these two related art configurations, all the mail pieces for a route would be loaded in the sorter, scanned, and put into clamps before the first piece was actually sorted. This allows the database management system to determine how many pieces of mail are destined for each address, and to calculate the total accumulated thicknesses of all the mail pieces destined for each address. With that information, the controller could then determine if one address station was sufficient to hold the mail to be delivered that day for each address. For example, in Europe, each address along a route receives an average of 2.5 mail pieces per day. So, it was assumed that the address stations would be designed with a capacity to hold 5 mail pieces. The sorter was designed for the clamps to fit onto a drive mechanism at fixed pitches of 0.2″. So, if all the mail pieces had thicknesses below the 0.2″ pitch, then each address station could hold five mail pieces. If there were some pieces that were thicker than the 0.2″ pitch, then two or more pitches would be assigned to that piece. Thus, for example, a 5 pitch storage system could handle five thin pieces, or three thin pieces and a thicker piece that required two pitches to store, or one thin piece, and two thicker pieces that each required two pitches to store, or a single thick piece that required all five pitches to store . . . and many other combinations. Since the controller counts the number of pieces and measures the thickness of each piece while they are being loaded into the clamps prior to the sorting operation, the controller can determine if the combination of the number of pieces and the accumulated thickness of the pieces destined for a particular address will exceed the storage capacity of an address station. If more than one address station is required to handle the mail for a particular address, the controller would assign two or more adjacent stations to handle the mail for that address during the sorting operation—and thereby keep the mail in delivery sequence order. That is why (in the above examples), for routes with an average of 600 addresses, a total of 800 addressing stations were provided—to handle heavy mail days. Reading the addresses for all the mail in a particular route, before starting to sort the mail, makes it possible for the controller to not assign an address station to an address for which no mail is destined.
The first of the two configuration described above had 80 diverters, and required a relatively long job time, but the cost was relatively low. In the second configuration with 800 diverters, the job time is quite fast, but the cost of the sorter increases approximately by a factor of at least ten. It would be highly desireable to somehow combine the low cost of the first configuration with the speed of the second configuration.
The architectures of the above-described configurations are not particularly space-efficient. Each address station requires two types of spaces: a blank space at the beginning of each address station to keep an open gap to allow mail pieces to be moved into the address storage area without colliding with mail pieces that are already there.
Typically, 3″ or 15 pitches of open area are required to prevent collisions with incoming mail pieces. Furthermore, space is needed for storing the mail being sorted to that address. If a system is designed to store 5 mail pieces at 0.2″/pitch, this will add another inch of space. So the total space for each address station will be 4″. If the storage capacity is increased from 5 to 10 pieces, another inch of storage space will be required, and the total space will be 5″. It is obvious that the need to have the 3″ of empty space for moving mail pieces to each of the address storage areas makes the sorting stations quite inefficient in space usage. The need to read all the mail for a particular route before starting the sorting operation has a disadvantage of requiring storage space for the average of 1500 pieces per route after the mail is clamped, but before the sorting operation begins.